Help Me Clarify My Understanding of Ionizing Radiation

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Help Me Clarify My Understanding of Ionizing Radiation

Post by Broomstick » 2018-07-31 01:13pm

I have recently been reading about radiation exposure, from Marie Curie's isolation and study of radium in the 1890's to the horrible fate of the "Radium Girls", Eben Byers, and the guy who developed the radium paint used for watch and instrument dials in the early part of the 20th Century, to the atomic bomb era, Cold War, various accidents.... Not that it was all about death and destruction. Smoke detectors have saved many lives with little risk to the users and most depend on Americium, there's all sorts of medical imaging, judicious use of radiation in medicine, in detecting weaknesses in aircraft parts before failure and death...

Anyhow - there's all sorts of varieties of radiation. I just want to be sure I have a handle on some of it.

Mostly, I'm talking here about ionizing radiation, not things like light.

There are alpha-emitter, which, well, emit alpha particles. Alpha radiation is basically a bare-ass helium nucleus. It can cause damage to living tissue but is easily blocked by minimal barriers, like the dead skin cells that form the surface of your skin. The biggest problem is if alpha-emitters get into your body where your living cells have no barrier between them and the bouncing alpha particle. Given their (relatively) high mass they can be extremely dangerous once in the body because their high mass means they can do a lot of damage compared to other radioactive particles. Then they can cause all sorts of havoc. To deal with alpha-emitters in your environment you don't eat the local food, don't drink the water, and don't drink the air. Yes, you wear a serious hazmat suit. A thorough shower of said suit followed by careful removal should be all the protection you need.

Beta-particles are basically rampaging electrons OR positrons (hey! anti-matter! How cool! How Star Trek!) They are more penetrating than alphas, less so than gammas. A thin metal plate can stop them, but they will get through your skin. This is where a "lead suit" type of hazmat gear could be useful even if pretty damn heavy. So... fantastic! We can protect again alpha and beta! (Albeit with come inconvenience and trouble). Betas are harder to shield from, but if they get inside the body may not be as damaging as alphas do to having almost no mass.

Another analogy - alphas are like cannonballs - they don't move terribly fast, but their mass winds up transferring a lot of energy to whatever they hit causing a great deal of damage. Betas are like BB's - even when a LOT faster/energetic than alphas they're so small and have so little mass they aren't likely to cause fatalities unless you get his by a LOT of them or have the bad luck to get hit in just the right spot to cause a catastrophe. Yes, it's a flawed analogy so if you've got something better or can improve it go right ahead.

Something I only recently learned about betas is that when you shield against them and they go through the shielding material they slow down, and can emit gamma rays during the slow down. Also, the atomic weight of the material used as a shield also effects the energy level of those gamma rays. So it's actually safer to use a shield of, say, aluminum or wood than of lead because the gamma that results from beta slow down would be less from the lighter shields than the lead. So maybe you don't want a lead hazmat suit, you really do want a hat made of tinfoil (aluminum) in that situation!

Gamma rays are photons. Really, really energetic photons. They are also really, really penetrating. They have uses in industry as, essentially, x-rays on steroids for imaging purposes because they go through a lot of stuff. Shielding against these guys is challenging although, fortunately for squishy creatures like us, the Earth's atmosphere does a pretty good job of filtering out a lot of gamma rays that would otherwise come to us from outer space.

What I'm still fuzzy on here, though, is the role that neutrons play in radiation. I know that shooting neutrons at atoms can cause changes in atomic number, which can cause all of the above sorts of radiation. The shooting neutrons come from atoms fissioning, right? Also from fusion? From matter/anti-matter interactions going >BOOM<?

In most cases, radiation doesn't cause a person or items to become radioactive, that's usually a case of people or things becoming contaminated with radioactive isotopes (hence, don't eat the food, don't drink the water, don't breathe the air, and take a shower). Under what circumstances does radiation cause the formation of radioactive isotopes in people and things? Gamma rays? Wandering neutrons? Is there something else I'm missing here?
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Re: Help Me Clarify My Understanding of Ionizing Radiation

Post by Eternal_Freedom » 2018-07-31 02:00pm

Alpha and Beta radiation can (IIRC my physics classes correctly) cause material to become radioactive, but it requires the alpha or beta particle to actually merge with the target nucleus and just happen to transmute it into an unstable radioactive isotope - and that's rare and difficult to do as alpha and beta are comparatively easily blocked.

Only neutrons really make targets materials radioactive and they're also a real bitch to shield against - because alpha and beta particles are electrically charged and so get deflected and/or can be bent/steered by magnetic fields (see the old cathode ray tube screens for any example of bending/steering electrons aka beta particles). Neutrons however are, well, neutral. SO they don't get deflected by electrostatic forces.

Shielding against neutrons means you want a lot of dense material between you and the source, since you basicaly have to hopethat one of the nuclei in the shielding material physically interposes between you and the oncoming neutrons, whereas with an alpha or beta you just have to get them close enough for electrostatic repulsion to do the trick.

In regards to your understanding, yeah, neutrons tend to be released from fission reactions - less so from fusion reactions though some neutron emission is still present. Matter/antimatter reactions shouldn't emit much in the way of neutrons, if only because it'll either be nothing but gamma/x rays or gamma and x rays as well as scattered atoms of the initial mass that didn't annihilate.

In sumary:

Alpha particles - highest-energy, lowest-penetrating. Essentially a ionised Helium-4 nuclei (two protons, two neutrons). Causes very nasty death if ingested. Can be stopped by a few centimetres of air or human skin.

Beta particles - electrons or positrons. Mid-energy, mid-penetration. Dangerous but can still be blocked by only a few layers of aluminium foil - or sheets of paper (IIRC it's used as a way to test paper thickness, if beta particles get detected the paper isn't too thick)

Gamma rays - very high frequency, low wavelength photons. Lowest energy (for most sources!) but highest penetration. Shielding usually requires about a foot of lead or other heavy metal - my physics described the difference alpha particles and gamma rays as being punched by a boxing glove and stabbed by a stiletto blade - the punch has a lot more kinetic energy and momentum but can basically be shrugged off, the stiletto,not so much.

Neutrons are nasty things. Penetrative, ionising, can induce radioactivity in stuff it hits, a right bitch to shield against (and again IIRC proper neutron shielding needs a different material to gamma shielding, so you can't have one size fits all) and can be highly energetic.

Though it's worth remembering that you don't need your shield to stop all the radiation as that's impractical, you need it to shield enough of the radiation that the rest isn't a threat if properly managed, and some simply tricks like being further away greatly reduce the effect thanks to the inverse square law - if you're twice as far from a gamma source as someone else, you absorb only one quarter the radiation, if you're ten times further away it's just one percent.
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Re: Help Me Clarify My Understanding of Ionizing Radiation

Post by Imperial528 » 2018-07-31 02:01pm

Neutron capture from neutron bombardment is generally what makes a material radioactive. Under the right circumstances high-energy gamma rays can also induce radioactivity, if they collide with the nucleus and have enough energy to knock a portion of the nucleus, usually a proton or neutron, loose and thereby transmuting it into an unstable isotope or element.
Neutron radiation can also cause changes in molecular structure resulting in neutron embrittlement or neutron-induced swelling, usually in metals, as the neutrons dislocate atoms in the material during collisions.

Also, keep in mind that the higher UV spectra are also ionizing. I forget the exact cutoff but photons above a certain energy are able to induce electron emission when colliding with atoms, hence ionizing.

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Re: Help Me Clarify My Understanding of Ionizing Radiation

Post by Broomstick » 2018-07-31 05:21pm

I think x-rays are the bottom range of ionizing radiation - they certainly can cause burns, damage, and induce cancer with too much exposure.

Is there a name for "neutron rays" like there is for alpha or beta particles? Or do we just talk about loose neutrons?

Is neutron embrittlement where neutron bombardment turns metal atoms into something else, result in a loss of metal and change in structure? Or is it something else? Never hear of "neutron swelling" - is that caused by metal atoms becoming something else? Or are we talking about neutron impacts disrupting the structure of the metal, slightly moving atoms out of alignment, disrupting the micro-crystalline structures? Or is it a combination of things?
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Re: Help Me Clarify My Understanding of Ionizing Radiation

Post by Lord Revan » 2018-07-31 08:22pm

Broomstick wrote:
2018-07-31 05:21pm
I think x-rays are the bottom range of ionizing radiation - they certainly can cause burns, damage, and induce cancer with too much exposure.

Is there a name for "neutron rays" like there is for alpha or beta particles? Or do we just talk about loose neutrons?

Is neutron embrittlement where neutron bombardment turns metal atoms into something else, result in a loss of metal and change in structure? Or is it something else? Never hear of "neutron swelling" - is that caused by metal atoms becoming something else? Or are we talking about neutron impacts disrupting the structure of the metal, slightly moving atoms out of alignment, disrupting the micro-crystalline structures? Or is it a combination of things?
as far as I know neutron radiation is called just loose neutrons.

X-rays and gamma rays are lower energy density then alpha and beta but are a lot more penetrative (sic) due being electro-magnetic in nature. As a (very rough) rule of thumb you can block alpha radiation with thick piece of paper and beta with a decent sized wood fence but you need thick walls of solid lead to "block" gamma radition to point that you can safely stand on the other side. It should be noted that nuclear plants don't use lead but other lesser materials but also you're not suppose to stand right next to reactor while it's active.

that damage from Alpha or beta radiation is generally close to the surface while x-rays or gamma rays fuck up everything.
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Re: Help Me Clarify My Understanding of Ionizing Radiation

Post by Imperial528 » 2018-07-31 08:31pm

Whether light is ionizing depends on the material, for standards the FCC starts ionizing at 10eV, equivalent to a wavelength of 124nm, which is in the far ultraviolet. Other standards use 33ev which is at 38nm wavelength and very close to the boundary between ultraviolet and x-ray. Essentially x-rays are ionizing to all materials whereas only the higher ultraviolet wavelengths are.

The name for neutron radiation is just neutron radiation.

Embrittlement in the long term will be from some transmuting of the material introducing defects but it is mostly due to the neutrons knocking the atoms around and messing with the molecular alignment. Neutron bombardment changes the molecular structures, potentially increasing or decreasing density and affecting the properties of the metal. Brittleness results from scattered defects in what was once a homogenous or otherwise orderly material causing it to respond less effectively to forces. The change in density also results in a change in volume, which is the swelling.

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Re: Help Me Clarify My Understanding of Ionizing Radiation

Post by LaCroix » 2018-08-01 06:16am

Neutron embrittlement in metals:

First some general metallurgy (simplified)...

Metals gain their strength due to 3 factors:

Their neat alignment in grids/lattice of identical atoms. Some materials have more/stronger bonds than others, resulting in the base hardness of the pure material.

Adding other metals creates an alloy - the result of the different atoms bonding together in vastly different lattices can create materials much harder than the base elements-

Adding (non-metallic) impurities that are suspended in between these "grid webbing". That is the interesting part.

In case of steel, for example, it is mostly carbon atoms (among other elements that either alloy with the iron or act as impurities) that give the hardness, by pre-stressing the grid due to their presence. The more C atoms there are, the more stress there is in the lattice. As long as there are some non-stressed connections to contract and even the general stress out, the lattice will become much harder, due to as a whole being less "compressible".(The impurities acts as a "rebar" in the metal "concrete", making the lattice flex less.)

At a certain amount of impurities, the stress in the lattice surpasses a point where the "pure" areas of the material can make up for the extra space needed by the "balloning" impurity-stressed ones. That means while still being very hard, it becomes prone to shear at these overstressed areas. You turned high-carbon tool steel into cast iron. Really hard, but brittle.

Something similar happens during heat treatment (oversimplified) - the process increases the amount of stress in the lattice due to first "relaxing/stretching" the lattice by adding energy (heat), and then rapidly constricting the lattice by cooling. This results in not only having the impurities, but also leaves the grid little time to cool and realign neatly, resulting an out-of square lattice which adds extra stress in the material, as if you added more impurities, and also causing more brittleness. By carefully reheating, you allow the worst disalignment to shift and lessen, relieving a certain amount of this stress, leaving you with a hard, and less brittle, useful material.

Neutrons randomly getting into, and absorbed by metal act a lot like heat treatment. Adding neutrons to single atoms of the lattice means that they get bigger. They simply need slightly more space, distorting the lattice by pushing their neighbors out. This causes stress, just like stress induced by the sudden cooling during quenching. The material will swell, and if it can't, or doesn't gets stress relief by some kind of heat treatment, allowing the swelling to increase even more in order to reduce the stress, then then over time, more and more areas with bigger atoms are generated all over the material, which causes the very same overstressed/shearprone areas in the material that we call brittleness.
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Re: Help Me Clarify My Understanding of Ionizing Radiation

Post by Napoleon the Clown » 2018-08-02 04:24am

It should be noted that inducing radioactivity in a previously stable atom is quite difficult. You need to change the nucleus itself. You can 100% ionize it and you're going to have an absurdly reactive little atom on your hands but it won't emit radiation.

Radioisotopes arise when there's not the right combination of neutrons and protons in the nucleus. Neutrons, on their own, don't want to remain neutrons. They will spontaneously decay with a half-life of something like 11 minutes. Typical decay of a neutron is to spit out a neutrino, photon radiation, and an electron. The result is a proton, neutron, and energy release. We can generally ignore neutrinos. If a neutron has proton buddies, it's content to exist if things are balanced. Through means I am not at all familiar with, the happy combinations vary all over the place. Off-hand I know that hydrogen, helium, carbon, and oxygen each have to stable isotopes. Fluorine has one. Some elements have many stable isotopes. Bismuth and heavier have no stable isotopes, though the half-life of bismuth is so incredibly long that it can be considered stable for all practical purposes. So yeah, too neutron-heavy and the neutrons want to decay. Too proton-heavy and the protons repel each other enough that you end up seeing some make a break for it.

Mechanisms to throw a stable isotope out of balance involve adding protons and/or neutrons to the nucleus or removing them. Adding is extremely difficult, because you need some pretty strict circumstances. Energies have to be in a pretty narrow window, collisions have to be just right... And even then, it takes truly absurd amounts of energy to "guarantee" that fusion happens. Fusion reactions quite often involve the decidedly odd properties of subatomic particles being able to just kinda... bypass energy levels sometimes.

Fission (knocking part of the nucleus off) is less hard, but still hard. Once again, you get into some pretty narrow ranges of conditions under which the desired result occurs.

In either case, if the resulting atom is a radioisotope of some atom, you get radioactivity. To cause meaningful radioactivity, you need to do this to a lot of atoms. If you only transmute one atom into something with a half-life in the order of a thousand years, you might still have that same atom a thousand years hence. 50% chance, basically. More likely is for already radioactive atoms to end up forming bonds. Nuclear weapons, be they fission, fusion, or just "dirty" bombs, throw radioisotopes all over the damn place. Some induced radioactivity likely occurs, but it's negligible compared to the 10 kg of U-235 or Pu-239 (as just one possible figure) that went into constructing the bomb.

tl;dr: Making an atom itself become a radioisotope is hard. You basically have to go out of your way to do it, because you're transmuting an atomic nucleus. The strong and weak force are both incredibly difficult to overcome. Even nuclear warheads (or the core of our sun) technically cannot overcome the energy barrier. They accomplish it because quantum physics is fucking weird. The exceeding majority of atomic nuclei fragments that strike another atom bounce off, imparting energy in the process but not actually altering the nucleus of the atom struck. Think of it as playing darts on a really hard board. You need to throw it at a good angle with enough force for it to stick, but throw it too hard and it's going to rebound out again. Throw it at a bad angle and it'll bounce as well.
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